Now we enter the heretofore-murky waters of liking, wanting, and “food reward”.

(Part VI of a series. Go back to Part I, Part II, Part III, Part IV, or Part V—or go on to Part VII.)

Summary: The Story Thus Far

In previous installments, we’ve established the following:

• Hunger is not a singular motivation: it is the interaction of several different clinically measurable, provably distinct mental and physical processes.
• In a properly functioning human animal, likes and wants coincide; satiation is an accurate predictor of satiety; and the combination of hunger signals (likes and wants) and satisfaction signals (satiation and satiety) results in energy and nutrient balance at a healthy weight and body composition.
• Restrained eating requires the exercise of willpower to override likes, wants, and the lack of satiation or satiety; the exercise of willpower uses energy and causes stress; and stress makes you eat more. Therefore, a successful diet must minimize the role of willpower.
• A lack of satiety will leave us hungry no matter what else we do to compensate. We fail to achieve satiety by not ingesting (or not absorbing) the energy and/or nutrients our body requires, and by an inability to retrieve the energy and/or nutrients our bodies have stored due to mitochondrial dysfunction.
• Satiation is an estimate of future satiety based on sensory input. As with satiety, we fail to achieve it by not satisfying our nutritional needs. We can also bypass satiation by decreasing sensory exposure to our foods. Some common enablers are eating quickly, eating while distracted or on the run, and eating calorie-dense packaged and prepared foods.

A Disclaimer

I’ve put off writing these next few articles because they’re likely to cause some controversy, which I don’t enjoy. My objective with the articles I write here at gnolls.org is to organize, distill, and summarize the bewildering variety of nutritional information into succinct, helpful articles, to share them with my readers, and to improve them as new information comes to my attention.

(An aside: I thank you, my readers, for continuing to provide references, intriguing leads, and constructive criticism. Please continue to do so.)

Please note that I have no horse in any of the current races: I am neither selling diet books nor defending a career-building hypothesis, and my current series of articles started long before the AHS and any still-simmering disputes.

Finally, and most importantly, I am not proposing any new theories of hunger or obesity. The current literature is both comprehensive and, I believe, more than adequate to explain and understand observed phenomena.

That being said: let’s get started!

Endless Arguments Are Often A Sign Of Murky Definitions

When, after innumerable posts and presentations on the subject, we see very smart people unable to articulate exactly what is meant by fundamental concepts like “palatability”, it’s quite likely that the hypothesis in question is poorly specified.

Therefore, I will briefly summarize the current state of scientific knowledge, as I understand it, on the subject of hunger and reward.

Defining Our Terms: “Liking” = Hedonic Impact, “Wanting” = Incentive Salience

Though the terms “liking” and “wanting” seem reasonably self-explanatory, we must be careful when using them in the scientific sense.

When we speak of “liking” something, we’re consciously predicting our future reactions. (“I like eggs.”) However, in the scientific literature, “liking” refers only to our actual reactions of pleasure, both conscious and unconscious—the hedonic impact of an experience.

Similarly, when we speak of “wanting”, we’re consciously predicting our future likelihood of seeking out an experience. But again, in the scientific literature, “wanting” refers only to our actual motivation to do so—the incentive salience of an experience.

Curr Opin Pharmacol. 2009 Feb;9(1):65-73. Epub 2009 Jan 21.
Dissecting components of reward: ‘liking’, ‘wanting’, and learning.
Berridge KC, Robinson TE, Aldridge JW.
[Note: free full text]

In recent years significant progress has been made delineating the psychological components of reward and their underlying neural mechanisms. Here we briefly highlight findings on three dissociable psychological components of reward: ‘liking’ (hedonic impact), ‘wanting’ (incentive salience), and learning (predictive associations and cognitions).

The concept of “palatability” can be understood as the hedonic reward of food:

For most people a ‘reward’ is something desired because it produces a conscious experience of pleasure — and thus the term may be used to refer to the psychological and neurobiological events that produce subjective pleasure. But evidence suggests that subjective pleasure is but one component of reward, and that rewards may influence behavior even in the absence of being consciously aware of them. Indeed, introspection can actually sometimes lead to confusion about the extent to which rewards are liked, whereas immediate reactions may be more accurate [1]. In the extreme, even unconscious or implicit ‘liking’ reactions to hedonic stimuli can be measured in behavior or physiology without conscious feelings of pleasure (e.g. after a subliminally brief display of a happy facial expression or a very low dose of intravenous cocaine) [2,3].
–Ibid.

And when most of us think of “food reward”, we are thinking purely of “wanting”—specifically “incentive salience”:

By ‘wanting’, we mean incentive salience, a type of incentive motivation that promotes approach toward and consumption of rewards, and which has distinct psychological and neurobiological features. For example, incentive salience is distinguishable from more cognitive forms of desire meant by the ordinary word, wanting, that involve declarative goals or explicit expectations of future outcomes, and which are largely mediated by cortical circuits [34–37].

By comparison, incentive salience is mediated by more subcortically weighted neural systems that include mesolimbic dopamine projections, does not require elaborate cognitive expectations and is focused more directly on reward-related stimuli [34,35,38]. In cases such as addiction, involving incentive-sensitization, the difference between incentive salience and more cognitive desires can sometimes lead to what could be called irrational ‘wanting’: that is, a ‘want’ for what is not cognitively wanted, caused by excessive incentive salience [39•,40•,41]. [emphasis mine]
–Ibid.

That explains quite a bit right there, doesn’t it?

I’d love to quote more of Berridge et.al.—but as the full text is available for free, I’ll just recommend that you read it if you’re interested in digging into the details.

It should now be clear that “food reward” has three distinct components which we must distinguish and define if we hope to understand it:

• The hedonic impact of eating food: its palatability.
• Incentive salience: the drive to consume more food.
• The process of learning, in which both hedonic impact and incentive salience are modified by experience.

If we fail to separate these components, we find ourselves creating tautologies. For example, it’s obviously absurd to say alcoholism is caused by “alcohol reward”—but if we distinguish the hedonic impact of alcohol from the incentive salience of alcohol, suddenly we have a handle by which to grasp the issues and make headway.

Intermission

Some Important Observations About Liking, Wanting, and Learning

Here are what I believe are some important takeaways from the literature as they apply to hunger:

• Reward is not a concept limited to food. Common sources of reward in everyday life also include social approval from parents, friends, co-workers, and strangers; legal and illegal drugs; physical activities, such as recreational sports; successful accomplishment of tasks; and media consumption, including television and the Internet. Anything we “like”—anything with hedonic impact—is capable of creating and reinforcing a “want” for more—incentive salience.
      In fact, much of the literature studies drug reward (legal and illegal). These are easier cases to study, since the human body has no nutritional requirement for nicotine, alcohol, or cocaine, and reward is not tied up with other motivations.
• Taste is not the only determinant of hedonic impact. The circumstances surrounding consumption, such as social approval, are also powerful determinants…and they don’t even have to be associated with consumption!
      For example, beer is generally an acquired taste: most of us instinctively dislike its bitterness, and only ‘develop a taste’ for beer as we associate beer drinking with intoxication and positive social interactions. Note the universal context of beer commercials: beer = fun times with friends. Also note that advertising can drive consumption, despite having no association with the actual action of consumption.
      Another example: many Muslims and Jews are repulsed by even the thought of pork purely due to social context, despite having no intrinsic inability to ingest or digest it.
• Incentive salience (“wanting”) is not an intrinsic property of food, or anything else. Unlike our instinctive aversion to spiders, humans have no instinctual knowledge of Pringles, Twizzlers, or Cinnabons. Incentive salience is a learned property.
• Therefore, incentive salience (“wanting”) is not a static property. It is created and reinforced by the hedonic impact (“liking”) of food consumption itself, by the positive experiences of satiation and satiety that consumption of nutritious food can produce, and by its associations with other rewarding factors and experiences (as enumerated above).
• We must distinguish experiences that modify hedonic impact (“liking”) or incentive salience (“wanting”) from incentive salience itself. For instance, the fact that the satiety response can modify incentive salience does not make satiety part of the reward response.
      It’s even easier to understand this error when we understand that social context affects hedonic impact: it’s clearly silly to call social relationships part of “food reward”. This error has been a major source of confusion in the discussion so far.

Conclusion

In order to understand the role of “food reward” in hunger, we must define and distinguish its constituent motivations:

• The hedonic impact of eating food: its palatability.
• Incentive salience: the drive to consume more food.
• The process of learning, in which both hedonic impact and incentive salience are modified by experience.

Further, we must understand that reward is not limited to food, is neither static nor an intrinsic property of the food itself, and is modified by many experiences besides its taste during the act of consumption—most of which are not themselves reward pathways.

We’ll start exploring these motivations and interactions—and how they fail—in Part VII. Click here to keep reading!

Live in freedom, live in beauty.

JS

(Part VI of a series. Go back to Part I, Part II, Part III, Part IV, or Part V—or go on to Part VII.)

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